The invention is base on a fuel injection pump for an internal combustion engine. In a known fuel injection pump of this type (German Offenlegungsschrift No. 30 17 276), the control groove is disposed obliquely in the jacked face with respect to the axis of the distributor, so that upon a displacement of the distributor the onset of filling or the end of injection during the injection stroke can be varied. To control the quantity injected, a pre-storage reservoir of variable volume is provided, from which the fuel is delivered to the pump work chamber during the intake stroke controlled by the control groove. The adjusting mechanisms for the variable reservoir plus an additional electrical adjusting device represents considerable expenditure for this form of embodiment. Futhermore, an additional expense must be undergone for controlling the supply of the pre-storage reservoir in cycles synchronized with the pump rpm.
In an injection device known from German Offenlengungsschrift No. 19 19 969, the fuel quantity which is supposed to be injected during the supply stroke of the pump piston of an injection pump is metered in a simplified manner upon the intake stroke of the pump piston by means of a magnetic valve controlled in a clocked or an analog manner. A pre-storage reservoir is thus unnecessary. The metering quantity is determined by the opening time of the magnetic valve, and the opening phase of this valve takes place solely within the time period in which the intake stroke of the pump piston occurs. In this known device, pressure conditions in the work chamber and the valve cross section of the fuel injection pump affect the metering quantity. For precise metering of the fuel injection quantity, the rpm and the instant of injection must be taken into consideration when designing the duration of opening of the magnetic valve. Pressure fluctuations in the work chamber during the filling process must also be taken into consideration. Further disadvantages of the known device are a result of the limited switching speed of a magnetic valve. The two switching events of the magnetic valve which take place during the metering phase during the intake stroke thus affect the precision of the result of metering. Furthermore, limits are placed upon the rpm or the pump rpm by the switching time of the magnetic valve.
In another fuel injection pump, known from German Offenlegungsschrift No. 19 19 707, the limited switching speed of magnetic valves was taken into account by providing, in this distributor injection pump, that two pump systems are accommodated in the distributor, each being supplied with fuel via one magnetic valve. In this manner, a high pump rpm is attainable. Furthermore, in this injection pump the cam drive of the pump pistons is embodied such that the stroke speed of the pump piston is substantially less during the intake stroke than during the supply stroke. The magnatic valve of each pump system of this radial piston pump is in any case opened solely during the intake stroke of the pump piston, and the opening duration of the magnetic valve determines the metering. Here again, the rpm and the adjustment of the instant of injection must be taken into consideration in controlling the magnetic valves. In the design of this pump, the metering cycle of the magnetic valve begins with the intake stroke of the associated pump piston. An adjustment of the injection onset necessitates a change in the onset of the intake stroke, so that the latter must be stated precisely when calculating the opening time of the magnetic valve. In so doing, however, the dynamic conditions prevailing at the reversal point of the pump piston during the transition from the supply stroke to the intake stroke are very difficult to control.